1. Field of the Invention
The invention relates to a gas discharge tube, in particular, a surge voltage arrester, having a gas-filled housing in which main electrodes are disposed opposite one another, supported in a gas-tight fashion by the ends of a tubular insulating member. At least one strip of electrically conductive material, as an ignition strip, extends over a portion of the length of the interior of the tubular insulating member.
2. The Prior Art
Surge voltage arresters, of this general type are known and described, for example, in the German AS No. 2,207,009 or the German AS No. 2,346,174.
The ignition voltage of surge voltage arresters should be as independent as possible upon the rate of voltage rise dV/dt. In known surge arresters, this is to some extent the case, up to approximately 10.sup.6 V/sec. In the case of high voltage rise speeds; i.e., above 10.sup.8 V/sec., however, one finds markedly higher ignition voltages, such voltages being referred to in the following as the impulse breakdown voltage.
The impulse breakdown voltage can be significantly reduced by the use of radioactive materials; for example, tritium, added to the gas or by using ignition strips or electrically conductive coatings on the interior walls of the insulating member of the surge voltage arresters. It is necessary to maintain a distance of at least 1 mm, however, between the trigger line and one of the main electrodes, to maintain insulating values above 10.sup.10 ohms between the main electrodes.
The length of this insulating distance markedly influences the impulse breakdown voltage in such a manner that the arresters with the shortest insulating distances (and therefore the highest field intensity at the tip of the ignition strip) are the most rapid with the lowest impulse breakdown voltage. However, it is difficult to establish a small distance precisely, since, particularly in the case of insulating tubular members formed of glass, the main electrodes are pushed into the softened glass against the ignition strip tip in a somewhat variable manner. This leads to a considerable variation in the surge voltage arrester characteristic values.